Preheat the oven to 350 degrees F. Grease a 24-cup mini muffin tin with nonstick cooking spray. Fill the cups half full with the sprinkle cookie dough. Bake for 12-14 minutes, or until the edges are golden brown, but the center is still soft. Let the cookies cool in the pan for about 5 minutes, then carefully transfer to a cooling rack to cool completely. The middles will sink and that is ok. Repeat with remaining dough.

While the cookie cups are cooling, make the vanilla buttercream frosting. Using a stand mixer or handheld mixer, beat the butter on medium speed until creamy, about 2-3 minutes. With the mixer on low, add 4 cups confectioners' sugar, the heavy cream, and vanilla extract. Turn up the speed to high and beat for 2-3 minutes or until frosting is smooth. If the frosting is too thin, add 1/2-1 cup more confectioners' sugar and beat again. If the frosting is too thick, you can thin it out with a little extra heavy cream. Only add 1 tablespoon at a time.

Pipe the frosting onto the cookie cups and decorate with additional sprinkles. Serve and enjoy!